Semantic and phonological context effects in visual search

Abstract

Visual search requires participants to search for a pre-specified target amongst a number of distractors. According to theories of visual search, attention is directed towards the target through a combination of stimulus-driven (bottom-up) and goal-driven (top-down) means. For example, when searching for a red car, top-down attention can prepare the visual system to prioritise items with matching visual properties to the target, e.g., red objects. Theories of visual search support guidance according to visual properties, including the Guided Search model (Wolfe, 1994) and Attentional Engagement Theory (AET: Duncan & Humphreys, 1989). However, whether or not attention can be guided according to non-visual properties of the stimulus, such as semantic and name information, remains controversial (Wolfe & Horowitz, 1994). This thesis studied search for a target (e.g., baseball-bat) in the presence of semantically related (e.g., racquet), phonologically identical (homophones, e.g., animal-bat) and phonologically related distractors (e.g., bag). Participants’ reaction times (RTs), error rates, eye movements and event-related potentials (ERPs) were monitored, and performance compared between young, older adult and brain-damaged individuals. Chapters 2 to 4 report semantic interference for all participant groups; Chapter 5 reports homophone interference in young adults and Chapter 6 reports no interference of phonologically related distractors in search for the target by young adults. The results support search being guided according to semantic and whole-name information about the target only. The mechanisms involved in this interference and contributions of these findings to the theories of visual search will be discussed.